Orientation in the chlorination and bromination of phenylsilanes containing SiF₃ and Si(CH₃)₃ groups

Summary

• 1. In the chlorination of (CH₃)₃SiC₆H₅ and F₃SiC₆H₅ in presence of iron, the trimethylsilyl group is orthopara orienting and the trifluorosilyl group is powerfully meta orienting.

• 2. In the chlorination of phenylsilanes the replacement of alkyl groups attached to the silicon by the more highly electronegative chlorine or fluorine atoms leads to change from ortho-para orientation to meta orientation. The dichlorination of Cl₃SiC₆H₅ and of p-ClC₆H₄SiCl₃ results in the formation of a complex mixture of reaction products.

• 3. Unlike chlorination in presence of iron powder, photochemical chlorination of (CH₃)₃SiC₆H₅ occurs only at the C-H bonds of the methyl groups.

• 4. Unlike the trichlorosilyl group, the trifluorosilyl groups and other groups directly attached to the aromatic nucleus are fairly readily eliminated during halogenation in presence of iron powder, which is evidently associated with the steric and induction effects of groups attached to silicon, with the electrophilic character of the silicon, and also with the ionic mechanism of the reactions.